Pulsus paradoxus (PP) is a valuable pathological vital sign in the management of asthma and in the rapid evaluation of patients with dyspnea in general. Early asthma management guidelines published by NHLBI in 1991 included a recommendation for physicians to measure PP in acutely asthmatic patients. Recent evidence continues to show that PP can play a role as a metric indicative of respiratory effort during dysfunction. Unlike peak flow rate and spirometry, PP measurement is non-effort dependent and would theoretically result in better assessment of asthma severity. Pulsus paradoxus is present in asthma, croup, and pericardial tamponade and tension pneumothorax. It appears prior to hypoxia in all of these conditions. For this reason, PP monitoring would prove useful not only to physicians but also to physician extenders who may be unfamiliar with the physiological dyscrasias of these conditions and would be assisted by an expert monitoring system. We propose 3 interconnecting specific aims: 1) Improve the automated PP detection algorithm resulting in at least a 95% agreement between automated PP and true PP measurement from a continuous non-invasive blood pressure monitor (NIBP). 2) Is the PP threshold of 12 mmHg for hospital admission in the 1991 NHLBI ED Asthma Management Guidelines valid as measured with an automated non-invasive PP monitor among acutely asthmatic children? 3) Is the PP threshold of 12 mmHg for hospital admission in the 1991 NHLBI ED Asthma management guidelines valid as measured with an automated non-invasive PP monitor among acutely asthmatic adults? In aim 1 we will improve upon our existing PP detection algorithm as it analyzes data in real time from a NIBP monitor. Aims 2 & 3 will test whether the original NHLBI emergency department asthma management guidelines, which included an actual PP threshold, are valid. Data from aims 2 & 3 will provide real world blood pressure data from acutely asthmatic patients for the iterative refinement efforts in aim 1. This Phase 1 effort will result in a refined PP monitor, for which we have a strong intellectual property position, and clinically relevant (validated) PP thresholds, which future asthma management guidelines will reference. Future Phase 2 activities could include prospective PP threshold testing in the emergency department and home monitoring of selected asthmatic patients, both of which would impact efficient clinical resource utilization.